MATLAB: Help me with a function.

matrixsum

I want to get a row matrix A from a parent row matrix B, where, the each component of A are the sequential sum of the components of B.

For e.g if B = [1 5 14 7 3] then A should be [1 6 20 27 30]

Please help.

Best Answer

A = cumsum(B);

Related Solutions

MATLAB: Sum across columns with shift

May be some other more clever indexing, but the "deadahead" thing that comes to mind if I understand the desire

>> a=1:18;a=reshape(a,6,[])     % sample smaller dataset for illustration...
a = 
     1     7    13
     2     8    14
     3     9    15
     4    10    16
     5    11    17
     6    12    18

The engine

[r,c]=size(a);                                        % get the array dimensions
b=arrayfun(@(i) sum(diag(flipud(a),i)),-(r-1):c-1);   % sum diagonals in desired sequence

Result

>> b
b =
     1     9    24    27    30    33    29    18
>>

ADDENDUM:

Somewhat cleaner is to subtract earlier for the indexing cleanup...

[r,c]=size(a)-1;                              % array dimensions less one for 0-base count
b=arrayfun(@(i) sum(diag(flipud(a),i)),r:c);  % sum diagonals in desired sequence

MATLAB: Reset value in cumsum matrix when reachin limit, and move the value to another matrix

First interpretation

I believe the OP wants to integrate over B but not allow the cumulative sum to exceed a threshold of 5. So "A" would be a vector not exceeding 5 while "C" would be a vector of 0s except for the values in "A" that were closest to 5.

% Example data
B = [1, 4, 3, 1, 3, 2, 1, 0, 0, 1, 5, 6, 9, 1, 3]; 
maxVal = 5;   % <-- set the threshold here
% Take the cumulative sum and convert it so that it doesn't exceed the 'maxVal'
A = cumsum(B); 
m = (0:maxVal:max(A))'; 
rm = (max(cumsum((A-m)>0))-1) .* maxVal;  %amount to remove
% Here's your new A vector
Anew = A-rm; 
% Here's your C vector
C = zeros(size(Anew)); 
C(diff(Anew) < 0) = Anew(diff(Anew) < 0);

Results

Anew =
     1     5     3     4     2     4     5     5     5     1     1     2     1     2     5
C =
     0     5     0     4     0     0     0     0     5     0     0     2     0     0     0

Second interpretation

(as described futher by OP in the comments below).

B = [1, 4, 3, 1, 3, 2, 1, 0, 0, 1, 5, 6, 9, 1, 3];
A = cumsum (B);
C = zeros(size(A)); 
for i = 1:length(A)
    if A(i) >= 5
        C(i) = A(i); 
        A(i:end) = A(i:end)-A(i); 
    end       
end

Results

A =
     1     0     3     4     0     2     3     3     3     4     0     0     0     1     4
C =
     0     5     0     0     7     0     0     0     0     0     9     6     9     0     0

Best Answer

Related Solutions

MATLAB: Sum across columns with shift

MATLAB: Reset value in cumsum matrix when reachin limit, and move the value to another matrix

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